In aerospace generally and aviation in particular, reducing the total fuel and equipment required to achieve a desired velocity, altitude, or operational envelope has long been sought.
Improving Operational Abilities
A variety of approaches have been taken to improve the operational abilities of aerospace vehicles. For example, many modern airplane fuselages are configured as monocoque or semi-monocoque structures wherein the exterior surface of the fuselage is also the primary load bearing member. This increases strength of the airplane while reducing the mass required for maintaining structural integrity. Thus, more mass can be devoted to useful payload (e.g., cargo, personnel, remote sensing equipment, weaponry, navigation equipment, communications equipment, fuel, and the like). Refinement, streamlining, and use of more efficient engines and wing profiles in modern aircraft (e.g., the Boeing 747®, available from The Boeing Company of Seattle, Wash.) has enabled vehicles with a useful payload fraction of 45 to 55%. Payload fraction, the measure of payload and fuel mass compared to total vehicle mass, has nearly doubled since the days of early propeller-driven aircraft.
While modern aircraft are very efficient, their design is optimized for taking off, ascending to a desired altitude, performing the required actions (e.g., crossing an ocean, surveilling an area), descending, and safely landing. Because aircraft are optimized for the entire flight path, they often do not achieve maximum efficiency during every stage of their operation. For example, an aircraft may be extremely efficient when landing, but inefficient when performing aerial surveillance from 50,000 feet.
Multi-stage vehicles partially address optimizing aerospace vehicle for their entire flight path. Multi-stage vehicles have long been used to efficiently transport and deliver payloads. A typical multi-stage vehicle comprises at least two stages, stacked one on top of the other. Each stage contains engines and propellant. The upper stage(s) contain operational payloads such as the crew, remote sensing equipment, weaponry, and the like. At launch, the first stage fires, lifting the vehicle into the air. Once the first stage runs out of propellant, it is jettisoned and the second stage ignites, carrying the payload to the desired location (e.g., a low earth orbit, an apogee, and the like). By jettisoning the lower stage(s) after it ceases operation, the vehicle reduces the remaining mass that must be carried to the desired location. Thus, the vehicle may use less fuel to get to the desired location. This also enables transport of larger payloads in the upper stage. Some multi-stage vehicles, like the Saturn V (operated by the National Aeronautics and Space Administration) or the Titan family of vehicles (operated by the United States Air Force, among others) utilize expendable stages. That is, each stage of the vehicle is designed for a single use. After this use the stage is jettisoned and destroyed or abandoned. While these vehicles may be optimized for each portion of their flight path, discarding stages after a single use is costly and severely curtails operational readiness because an entire new vehicle must be constructed and assembled after each use.
Other multi-stage vehicles, like the Space Shuttle (operated by the National Aeronautics and Space Administration), are partially reusable. That is, one or more stages of such vehicles are recovered and used again. While these vehicles avoid wasting the recovered stages, operational readiness is limited because of the significant processing time in between flights. Atlantis experienced the quickest turnaround of a Shuttle orbiter, as only 54 days lapsed between its launch on STS-51J and its launch on STS-61 B. Shuttle orbiter processing times were significant for many reasons, including the following: the Space Shuttle external tank (ET) was a single-use item, requiring a new ET to be built and tested for each flight; reusable portions of the Space Shuttle had to be recovered from their landing in the ocean; and the Space Shuttle was assembled and launched vertically, limiting the locations from which it could be processed and launched.
Shuttle orbiters, such as Atlantis, are lifting bodies, optimized for reentering the atmosphere and landing horizontally on a runway. The Space Shuttle is not optimized for other portions of the vehicle's flight path, however, because the orbiter does not provide aerodynamic lift during takeoff.
Emergence of Drone Aircraft
Unmanned and armed aircraft are known as “combat drones”. Such vehicles operate autonomously or semi-autonomously, flying to or from areas of interest with little or no human direction. Such vehicles may be remotely controlled by a pilot located off board the aircraft for use in combat zones. Combat drones may be controlled from remote locations several thousand miles away from their intended target, with a lag-time, or ‘latency,’ of only a few seconds. This unmanned style of combat has increased since its introduction in the early 2000s; an estimated 6,300 combat drones are currently used by the United States across the world.
Unmanned and unarmed aircraft are known as “surveillance drones”. Such vehicles may be autonomously controlled by onboard computers, may be under the remote control of an off board pilot, or may be controlled by a combination of the two. Surveillance drones may be used for surveillance by law enforcement and other government agencies within its own borders. The surveillance drone can also be used for stealth, data-gathering missions in combat zones. The elimination of a human pilot from the surveillance drone allows the aircraft to “loiter” in an area of interest for a significantly longer time than possible with an on-site human operator because the drone is not constrained by the physiological limits of a human pilot.
Surveillances drones are advancing in onboard technology offered, including onboard cameras with infrared technology, heat sensors and facial recognition capabilities.
Currently, the most advanced drones under development may takeoff using onboard jet engines. Once the drone reaches station altitude, the jet engine is powered-down, and the drone enters electric power mode. In electric power mode, the drone stays aloft via solar rechargeable electric battery-powered motors and propellers, and the engine provides no utility for the drone. In fact, the engine and fuel tanks are a detriment because such components have a significant mass and take up a significant amount of room within the cramped drone. Holding the dormant jet engine aloft places some drain on the drone's electric battery store.
Given the foregoing, what is needed are devices and methods which facilitate optimization of an aerospace vehicle during some or all phases of flight. Devices and methods which enable land-based recovery and reintegration of staged aerospace vehicles and aircraft are also needed. In particular, facilitating such recovery and reintegration without extensive ground support equipment is desired.
Additionally, devices and methods are needed which enable drones to: achieve a station altitude without an onboard jet engine or fuel tanks; reach station altitude with no power drain; and remain on station longer.